1. Field of the Invention
This invention relates to a compact variable focal length lens, and more particularly to a variable focal length lens assembly including a wide angle of which the number of lenses is about three to five, and which is suitable for a lens shutter camera or the like.
2. Description of the Prior Art
Compact cameras recently available include not only ones having a single focal length, but ones including a converter lens to switch the focal length and ones having a zoom lens mounted thereon. The demand for these variable power lenses has been increasing. However, such a variable power optical system is larger in size than a single focal lens, and has an increased number of lenses, which detracts from the compactness and lower cost of cameras.
For example, a camera encasing a converter lens is disclosed in Unexamined Published Japanese Patent Application No. 95210/1981. This camera includes a rear converter lens and the lens is mounted at the rear of a main lens at the long focal length. A total of six lenses are required to form the main lens and the converter lens. In unexamined Published Japanese Patent Application No. 201213/1982, a zoom lens is composed of 5 to 8 lenses. A simple zoom lens which has a relatively lesser number of lenses is disclosed in Unexamined Published Japanese Patent Application No. 48009/1985, which is composed of four lenses. In this case, however, when an attempt is made to increase the refracting power of a rear group to shorten an overall length, the curvature of a concave surface increases since the rear group comprises a meniscus lens, and a variation of spherical aberration at the time of variation of power increases. Consequently of which the spherical aberration becomes large in under correction on the wide angle side and in over at the telephoto end, and in addition, coating of the lens is difficult.
Furthermore, in the embodiment of the zoom lens, the focal length at a wide angle is 40 mm, which is somewhat too long for the wide angle lens. In order to make it into a wide angle, approximately 35 mm, off-axial aberrations need be further corrected, thus making it difficult to constitute the lens group only by four lenses.